DESCRIPTION: (Applicant's Abstract) The proposed experiments examine how subjects learn to control the movements of their hand in peripersonal space. We address these questions by analyzing trajectories and muscle activation patterns during movements aimed to targets presented in a virtual workspace. The experiments build on psychophysical results obtained in the current grant. These have demonstrated that the planning of hand movements is carried out in a vectorial space centered at the hand and that directional accuracy requires extrinsic information about initial hand position. The transformation of a vectorial hand-path plan into a motor program producing the necessary torques and rotations at joints requires a learned internal model of limb biomechanical properties. We now seek to identify the roles of sensory information in motor learning, using new paradigms for altering visumotor transformation and limb dynamics selectively. In the course of this study we will examine the feasibility of using auditory signals to provide information about joint and hand motions. We aim to answer four sets of questions: (1) How does information about movement errors adaptively alter the spatial representations used by subjects to plan movements extent and direction? (2) What characteristics of movements or limb properties are represented internally by the nervous system, to control inertial interaction? (3) What types of sensory information are most useful to the nervous system in updating its internal representations of the inertial properties of the limb? (4) What disturbances in movement execution, learning or the generation of inertial models of the lib are responsible for the inaccuracy of movements made by patients with cerebellar lesions? To answered there questions we examine the adaptation to altered displays of limb motions, and to alteration sin limb biomechanical properties are examined in three groups of subjects: normal controls, patients lacking proprioception (because of large-fiber sensory neuropathy), patients with localized cerebellar lesions. the use of auditory substitution of proprioceptive sensation to improve limb control in deafferented patients will be explored.